extracting mdf dust

[Barry Burgess]

Extracting from small machines:

The extractor's in a corner of the workshop. The felted polyester sock is about 2' in diameter x 5' tall. (about 32 sq') Airspeed through the filter medium is therefore about 38 ft/min. My understanding is that polyester felt will only trap the finest particles when the speed through the filter is 3-4ft/min or less**. No doubt a bigger filter is needed! About 10x bigger!

Ivan my pleated filters are 21metres squared which is 210 sq' and I am using 2. The sock approach is the main problem. The cyclones and drop buckets are there to reduce the amount of solid particles going to the filter. From what I can remember the area of filter should be at least 100sq' per HP

 

[Scrit]

Extracting from small machines:
My bag (sock filter) extractor is rated with bag (new, clean) and 6' of 6" flex hose, at 1200cu.ft./min and it barely captures all the dust made by the 10" RAS, which is hardly gigantic. When it gets a bit caked up flow is much less and effective extraction worse. The same applies to an Axminster horizontal belt sander. The bandsaw is clean if you extract from additional diy bottom rear, as well as just under table. There's no problem with the planer.

Ah, but what is the filter material rated at? And how long do you run it between cleanings? It sounds as though you might have a Chaiwanese 30 micron bag there which frankly will never give you decent results on fine dusts. Going to a 10 or even better a 5 micron sock filter and a larger/taller sock should result in a noticeable improvement in filtration. A decent sock will cost less then £25. The cleaner the inside of the sock filter, the greater the air flow, however the greater the amount of dust passed through the bag as the material is simply too coarse to trap it. In other words for maximum efficiency in absolute filtration terms the inside of your sock needs to be coated with fine dust....

The extractor's in a corner of the workshop. The felted polyester sock is about 2' in diameter x 5' tall. (about 32 sq')

If you go to a finer filtration material you may need to increase the filter surface area to reduce the back pressure in the extractor to levels where the machine continues to suck adequately. So, if you get a finer filter sock you should ideally try to get a bigger one, too. There is a rule off thumb sizing mechanism used for dust extraction which says that a 15:1 ratio (air flow in cfm to filter area square feet) is required in woodworking applications (don't know if that is on Bill's site but it is an industry accepted figure). Your filter at 32 square feet is therefore a tad undersized :shock: - going to a larger filter sock approaching the theoretical 80 square feet that 1200 cfm requires sounds like it will in itself alone improve the performance of the unit, because if it can blow 1200 cfm through such an undersized sock then the filter sock most be as open as a string vest - either that or the 1200cfm is a barefaced lie! In all probability the answer is something in between.

But you say that you don't have the space for bigger/extra socks - that leaves the only alternative as going to a cartridge filter from pleated spun-bond materials. One point overlooked in this discussion is the need to go for a pleated material which is not so tightly pleated that the pleats are blown flat when the unit is in operation as that would result in reduced available surface area within the filter.

The Q is, what can keep the bigger filter relatively clean- simple drop box or tricky to make cyclone.....

A cyclone is going to keep the filter material cleaner, without a doubt, because it spins out the waste centrifugally BEFORE the air reaces the filter material - much more efficiently than the "cyclone" bagger you have. The simplest reason for keeping the filter area as clean as possible is to reduce the annual time overhead for cleaning filters - and thereby reduce potential contact with fine dusts. That's not a vote in favour of ditching your bagger you'd probably find a decent pleated filter would improve the thing's performance dramatically.

BTW, even the spun bonded filter cartridges people here are discussing (such as Izumi-Cosma G2260 aka Axtar filter material) are frequently only 20 to 50% efficient for the sub 0.5 micron particles WHEN NEW. After the filter material has been loaded and cleaned a 3 or 4 times the efficiency starts to get up to the 85 to95% area (depending on particle size), with full efficiency being achieved around the 6 to 8 loadings area. so having a spotlessly clean filter surface area isn't the ideal, either. This is one particular material I've investigated, but others seem to show similar performance. As an aside I believe the technical desctiption for this filter material is "hydro-oleophobic 100% polyester spun bond". That's the washeable stuff, but it might be possible to find a pleated filter in an 80/20 blend "paper" material. These cannot be washed out, have a lower absolute strength and a correspondingly shorter lifespan but are quite a bit cheaper - and providing you don't get them wet they should work well in a part-time environment even though they are probably inadequate for an industrial/trade environment (or for that matter a workshop which is damp in winter).

Added note: I'd agree with Jake that the extraction ports on deWalt RASs are a joke. Even industrial machines like the Maggi and Stromab aren't brilliant, but if the hood given a larger port and a catcher hood is added to the rear of the saw then efficiency does improve.

Scrit

 

[Scrit]

From what I can remember the area of filter should be at least 100sq' per HP

I'll take issue with you on that Barry. The amount of energy required to draw a cubic metre of air through a system varies according to, amongst other things, the relative efficiency of the fan. Paddle fans (commonly used in baggers) are much less efficient that aerofoils (as used in filter envelope machines) which is why a 4kW aerofoil unit like my big unit seems underpowered against the 10HP (7.5kW) bagger unit I used to have, and yet it can keep the CNC router with 5 x 100mm ports clean - the bagger couldn't manage that. Fan curves tend to show that increasing the speed/power applied to a given size of fan has only limited effect on performance. The way to get increased flow is either to increase the size of the fan, otr increase its' efficiency. However as soon as you move away from the paddle fan blade (which can happily sit in a dirty airflow and be struck by debris) to a more efficient fan type, fan balance becomes critical and the fan blade needs to be located downstream of the filters to prevent it getting dirty and going out of balance - something that can destroy the bearings and may in extreme cases even result in disintegration (exploding) of the fan

Scrit

 

[Barry Burgess]

Scrit I was just considering non commercial bagged dust collectors. Airfoil for most of us require to much maintenance with the likely hood of them blocking if not checked regularly. I am playing with an impellor casing that I built at present. I am just using a clamp meter to see the amperage drawn by the motor - crude but that all I can afford for test kit. Most of the DIY extractors are running at about 50% of capacity as that cannot get rid of the air.- good for the warranty claims. The pleated filters do improve the efficiencies of the current systems. In the ideal world a ratio of cone lenght to body length should be 3 to 1 but at an 18" diameter that would produce a cyclone of 12 feet so not suitable for the garage

 

[Scrit]

Most of the DIY extractors are running at about 50% of capacity as that cannot get rid of the air.- good for the warranty claims. The pleated filters do improve the efficiencies of the current systems.

When I "upbagged" my double bagger 3 years back to much larger 2 micron socks I did the calcs and even on a commercial 3kW unit like ours the bags were grossly undersized. That unit is only used for chip collection, but upping the size of the bags made a huge difference to it - I reckon now it might be delivering near it's advertised 1900cfm and it can keep the machines it serves clean. It still not as good as a pleated filter or better still a cyclone IMHO. Maybe next year.....

Scrit

 

[ivan]

Thanks for your comments!

* filter media is singed polyester felt about 3mm thick. Presume the heat treatment makes the felt less fuzzy so most of the cake falls into the bin when you shake. All UK made and motored. Waste enters at top, bottom of felt sock connected to metal bin, plastic bag inside bin to aid emptying.

* Filter cakes up rapidly when cutting mdf, and you can easily tell the flow is much reduced.

* No, I probably don't clean it often enough; originally I had no trouble with fine dust coming through the filter sock, despite being aware of its size shortcomings. Began to see dust passing thro the felt when I began to use MDF. This now makes 'doing something' imperative.

* RAS guard port is 30x60 feeding 60mm hose, and a LP connection proves as good as twin 1kW motor vac. Hood behind is roughly 300x400mm and feeds 150mm pipe.

* A cartridge filter(s) would be convenient; previously looked a bit expensive (£180 each at Axminster) most pleased with Barry's cheaper find, even more pleased if most of his waste is going into his bins & bags.

* I hope my aside about Barry's cartridge filters hasn't confused the chap who started this thread!

 

[prawnking]

ivan you r right after reading all posts i am now completely confused to technical for me at the moment i thinks

i am thinking down the lines aof a trend T30af for now and building my own cyclone ready for when i get chance to upgrade extraction nozzles on my powertools

think io am going to buy a chip collector 1-1.5hp so when i am ready i can use the blower for my cyclone good idea or no?
cheers

shaun

 

[engineer one]

shaun i think you have got the thing right.

you have to start somewhere, and then upgrade as you discover
the shortcomings and what works properly for you.

it seems that for ordinary mortals, extraction is a difficult subject,
and you would have thought that buying a proprietory brand would
be a good first step, but unfortunately these days so much
is as scrit says built in chiwan that it is a price idea not a
performance one that is worried about.

you do wonder why no one makes a cyclone as a production item,
but then i guess the technical stuff is to complex to get things into
production at a sensible price performance ratio.

i think though that it is important to also were a mask when working
with machinery and manufactured boards.

good thread though

paul :wink:

 

[prawnking]

as a matter of interest is it mainly manufactured boards or is softwood and hardwood dust just as bad as mdf

shaun

 

[engineer one]

interesting we all thought so , but recently it seems that more and
more woods offer long term difficulties.

for those who can get a look, the latest issue of fine homebuilding
has an article about sealing rooms to protect from dust, or protect
the rest of the home from your work dust.

not sure whether it would be on their web site.

paul :wink:

 

[Scrit]

As a matter of interest is it mainly manufactured boards or is softwood and hardwood dust just as bad as mdf

The fineness of dust depends on the type of machine. For example sawing MDF isn't generally as bad as routing it. And the spindle moulder generally generates a lot less dust than a router will (another reason to have one!).

In dust terms MDF is probably the worst offender with some boards, such as Caberdecor (which I believe has more hardwood fibre content) worse than others, producing even fine dust. I don't find chipboard as bad, but I find some of the tropical hardwoods can also give me gip as do spalts.

Scrit

 

[Barry Burgess]

Prawnking
Buy the largest extractor you can afford. 2HP would be better- like me you could get that affliction of buying more tools - my next will be a thicknesser - all adding to the extractors load .
I am trying to find a cheap source of the basics for a cyclone so that woodworks don't have to become metal workers but it might be a pipe dream. I have hawked my plans around to many ducting shops with little success but I continue else I will have to learn a new skill. If you use 450mm pipes rather than 18" more is possible. I have completed all the woodwork for the stand and impellor but the metalwork is a mental block at present.
Barry

 

[Jake]

In dust terms MDF is probably the worst offender with some boards, such as Caberdecor (which I believe has more hardwood fibre content) worse than others, producing even fine dust. I don't find chipboard as bad, but I find some of the tropical hardwoods can also give me gip as do spalts.

The (only) thing I've ever had a noticeable reaction to is far-eastern wbp ply, which can give me an irritating dry cough moment. Nothing to any of the MDF I've used (edit: which doesn't, I think, include caber).

 

[engineer one]

barry let me add my engineering skill, you remember that's metalworking.
pm me and lets see what i can come up with as an idea, and whether we can productionise what you have in mind
paul :wink:

 

[Nick W]

Barry, Paul,

Have you seen the Clear Vue cyclones? They are made in the US but seem cheap enough to be worth investigating importing. Particulalry interesting is that you can buy just the bits you want.

I'm seriously considering getting one myself.

Usual disclaimers, no links etc...

 

[Barry Burgess]

Barry, Paul,

Have you seen the Clear Vue cyclones? They are made in the US but seem cheap enough to be worth investigating importing. Particulalry interesting is that you can buy just the bits you want.

I'm seriously considering getting one myself.

Usual disclaimers, no links etc...

Nick I have been in contact but the shipping costs are about the same price as the cyclone without the motor because of its cubed size.

 

[Nick W]

Oh poo.

 

[ivan]

Prawnking, I think Barry's right.
*my 1st extractor, an industrial vac, blocked up as soon as I got 1st stationary tool - improved it a bit, by fitting it onto small galv. dustbin with Camvac style large lower cloth filter.
*reported *worst* results from my present wall mounted sock filter extractor are earlier in thread. Try to avoid 'hobby' rated extractors and get the best 'trade' or small 'industrial'** rated one you can afford.
*Axminster claim their standard bag suitable for shavings/chips only, and their fine bag for sawdust and shavings. An mdf and sanding dust rating is not avalible by bag swapping, and adds considerably to the initial price.
* billpentz.com quote figures from a US heating and ventilation 'bible' which include 6"planer (270***), 6-12"planer(350), sander up to 6"belt (350), 12"disk sand(270), table saw not over 16" (350) bandsaw, blade up to 1/2" (200). These are "at the machine" figures.
* to achieve these under working conditions through pipe, filter cake, and half full bag you'd need twice this at the extractor for one machine
*As popular extractors seem to be rated with no bag or pipe at all, you'd need to look at something like 4 times these figs on the catalogue page, for one machine (as a rough rule of thumb)
* unless you're welathy, if you want an mdf dust rating, we'll have to follow in some version of Barry's diy footsteps.

** as per Axminster catalogue
*** figs. in cu.ft./min.

 

[Jake]

to achieve these under working conditions through pipe, filter cake, and half full bag you'd need twice this at the extractor for one machine

... with a standard LP extractor.

 

[ivan]

PS.
the figs. from the U.S. heating and ventilation 'bible' date back over 20 years to an age of innocence before the recognition of the need to capture finer particles. For DIY woodworkers you could take them as a minimum guideline.